Method and apparatus for transmitting data in wireless communication system

ABSTRACT

In an embodiment of the present invention, a method for indicating, by an access point (AP) associated with a first basic service set (BSS), spatial reuse (SR) in a wireless LAN (WLAN) system includes transmitting a trigger frame which requests uplink multi-user (UL MU) transmission of a plurality of stations (STAs) and receiving an UL MU physical protocol data unit (PPDU) generated based on the trigger frame from the plurality of STAs. The trigger frame may include SR indication information for indicating the SR of an overlapping BSS (OBSS) STA. The first high efficiency (HE)-signal (SIG) A field of the UL MU PPDU may include SR support information generated based on the SR indication information.

TECHNICAL FIELD

The present invention relates to a wireless communication system and,more particularly, to a method for transmitting spatial reuse supportinformation in order to support the spatial reuse of an OBSS AP/STA andan STA apparatus for performing the same.

BACKGROUND ART

Wi-Fi is a wireless local area network (WLAN) technology which enables adevice to access the Internet in a frequency band of 2.4 GHz, 5 GHz or60 GHz.

A WLAN is based on the institute of electrical and electronic engineers(IEEE) 802.11 standard. The wireless next generation standing committee(WNG SC) of IEEE 802.11 is an ad-hoc committee which is worried aboutthe next-generation wireless local area network (WLAN) in the medium tolonger term.

IEEE 802.11n has an object of increasing the speed and reliability of anetwork and extending the coverage of a wireless network. Morespecifically, IEEE 802.11n supports a high throughput (HT) providing amaximum data rate of 600 Mbps. Furthermore, in order to minimize atransfer error and to optimize a data rate, IEEE 802.11n is based on amultiple inputs and multiple outputs (MIMO) technology in which multipleantennas are used at both ends of a transmission unit and a receptionunit.

As the spread of a WLAN is activated and applications using the WLAN arediversified, in the next-generation WLAN system supporting a very highthroughput (VHT), IEEE 802.11ac has been newly enacted as the nextversion of an IEEE 802.11n WLAN system. IEEE 802.11ac supports a datarate of 1 Gbps or more through 80 MHz bandwidth transmission and/orhigher bandwidth transmission (e.g., 160 MHz), and chiefly operates in a5 GHz band.

Recently, a need for a new WLAN system for supporting a higherthroughput than a data rate supported by IEEE 802.11ac comes to thefore.

The scope of IEEE 802.11ax chiefly discussed in the next-generation WLANtask group called a so-called IEEE 802.11ax or high efficiency (HEW)WLAN includes 1) the improvement of an 802.11 physical (PHY) layer andmedium access control (MAC) layer in bands of 2.4 GHz, 5 GHz, etc., 2)the improvement of spectrum efficiency and area throughput, 3) theimprovement of performance in actual indoor and outdoor environments,such as an environment in which an interference source is present, adense heterogeneous network environment, and an environment in which ahigh user load is present and so on.

A scenario chiefly taken into consideration in IEEE 802.11ax is a denseenvironment in which many access points (APs) and many stations (STAs)are present. In IEEE 802.11ax, the improvement of spectrum efficiencyand area throughput is discussed in such a situation. More specifically,there is an interest in the improvement of substantial performance inoutdoor environments not greatly taken into consideration in existingWLANs in addition to indoor environments.

In IEEE 802.11ax, there is a great interest in scenarios, such aswireless offices, smart homes, stadiums, hotspots, andbuildings/apartments. The improvement of system performance in a denseenvironment in which many APs and many STAs are present is discussedbased on the corresponding scenarios.

In the future, it is expected in IEEE 802.11ax that the improvement ofsystem performance in an overlapping basic service set (OBSS)environment, the improvement of an outdoor environment, cellularoffloading, and so on rather than single link performance improvement ina single basic service set (BSS) will be actively discussed. Thedirectivity of such IEEE 802.11ax means that the next-generation WLANwill have a technical scope gradually similar to that of mobilecommunication. Recently, when considering a situation in which mobilecommunication and a WLAN technology are discussed together in smallcells and direct-to-direct (D2D) communication coverage, it is expectedthat the technological and business convergence of the next-generationWLAN based on IEEE 802.11ax and mobile communication will be furtheractivated.

DISCLOSURE Technical Problem

In the case of an existing system, CCA is performed based on a CCA levelthat is identically set in each BSS. That is, conventionally, a CCAlevel fixed for each BSS is applied. Accordingly, there is a problem inthat efficiency of spatial bandwidth reuse between BSSs is very low. Thereason for this is that STAs belonging to another BSS are all determinedto be a channel busy state because a fixed CCA level is applied to theSTAs even though the STAs are able to send signals depending on acommunication environment, channel quality, etc. and thus the STAs areunable to send signals.

Accordingly, in the next-generation systems, a technology for performingspatial reuse to which a dynamic CCA level capable of improving spatialreuse efficiency of a bandwidth is applied may be introduced. In thisspecification, there are proposed a method for supporting an OBSS AP/STAso that it performs spatial reuse and an STA apparatus for performingthe same.

Objects to be achieved by the present invention are not limited to theaforementioned objects, and those skilled in the art to which thepresent invention pertain may evidently understand various other objectsfrom the following description.

Technical Solution

In an embodiment of the present invention, a method for indicating, byan access point (AP) associated with a first basic service set (BSS),spatial reuse (SR) in a wireless LAN (WLAN) system includes sending atrigger frame which requests uplink multi-user (UL MU) transmission of aplurality of stations (STAs) and receiving an UL MU physical protocoldata unit (PPDU) generated based on the trigger frame from the pluralityof STAs. The trigger frame may include SR indication information forindicating the SR of an overlapping BSS (OBSS) STA. The first highefficiency (HE)-signal (SIG) A field of the UL MU PPDU may include SRsupport information generated based on the SR indication information.

Furthermore, the SR indication information may include controlinformation identically transmitted to the plurality of STAs so that theplurality of STAs generates the same SR support information.

Furthermore, the trigger frame may include a Common Info field includingcommon control information about a plurality of STAs receiving thetrigger frame and a Per User Info field including STA-specific controlinformation about each of the plurality of STAs. The SR indicationinformation may be included in the Common Info field of the triggerframe.

The method may further include receiving the second HE-SIG A field of aPPDU transmitted by an STA placed in a second BSS if the AP is placed inan OBSS in which the first BSS and the second BSS overlap, obtaining SRsupport information of the second HE-SIG A field, and performing the SRbased on the SR support information.

Furthermore, performing the SR may include adjusting a clear channelassessment (CCA) level and determining the busy or idle state of achannel based on the adjusted CCA level.

Furthermore, the SR support information may include at least one of SRpermission information of the OBSS STA, transmission power informationof the AP, and information about an interference level acceptable to theAP.

Furthermore, in another embodiment of the present invention, a methodfor indicating, by a station (STA) associated with a first basic serviceset (BSS), spatial reuse (SR) in a wireless LAN (WLAN) system includesreceiving a trigger frame which requests the uplink multi-user (UL MU)transmission of a plurality of stations (STAs) and generating an UL MUphysical protocol data unit (PPDU) generated based on the trigger framefrom the plurality of STAs. The trigger frame may include SR indicationinformation for indicating the SR of an overlapping BSS (OBSS) STA. Thefirst high efficiency (HE)-signal (SIG) A field of the UL MU PPDU mayinclude SR support information generated based on the SR indicationinformation.

Furthermore, the SR indication information may include controlinformation identically transmitted to the plurality of STAs so that theplurality of STAs generates the same SR support information.

Furthermore, the trigger frame may include a Common Info field includingcommon control information about a plurality of STAs receiving thetrigger frame and a Per User Info field including STA-specific controlinformation about each of the plurality of STAs. The SR supportinformation may be included in the Common Info field of the triggerframe.

The method may further include receiving the second HE-SIG A field of aPPDU transmitted by an STA placed in a second BSS if the STA is placedin an OBSS in which the first BSS and the second BSS overlap, obtainingSR support information of the second HE-SIG A field, and performing theSR based on the SR support information.

Furthermore, performing the SR may include adjusting a clear channelassessment (CCA) level and determining the busy or idle state of achannel based on the adjusted CCA level.

Furthermore, the SR support information may include at least one of SRpermission information of the OBSS STA, transmission power informationof the AP, and information about an interference level acceptable to theAP.

Furthermore, in another embodiment of the present invention, a station(STA) associated with a first basic service set (BSS) in a wireless LAN(WLAN) system includes a radio frequency (RF) unit configured totransmit and receive radio signals and a processor configured to controlthe RF unit. The STA may receive a trigger frame which requests theuplink multi-user (UL MU) transmission of a plurality of stations (STAs)and generates an UL MU physical protocol data unit (PPDU) generatedbased on the trigger frame from the plurality of STAs. The trigger framemay include SR indication information for indicating the SR of anoverlapping BSS (OBSS) STA. The first high efficiency (HE)-signal (SIG)A field of the UL MU PPDU may include SR support information generatedbased on the SR indication information.

Furthermore, the SR indication information may include controlinformation identically transmitted to the plurality of STAs so that theplurality of STAs generates the same SR support information.

Furthermore, if the STA is placed in an OBSS in which the first BSS anda second BSS overlap, the STA may receive the second HE-SIG A field of aPPDU transmitted by an STA placed in the second BSS, may obtain SRsupport information of the second HE-SIG A field, and may perform the SRbased on the SR support information.

Advantageous Effects

In accordance with an embodiment of the present invention, spatialbandwidth reuse efficiency between STAs belonging to an OBSS can beimproved. The adjustment of a CCA level is not fixed, but is dynamicallyperformed. Accordingly, a loss of communication performance can beminimized because a change in the state of STAs and a change in theenvironment of a channel between STAs are handled actively and rapidly.

Furthermore, in accordance with an embodiment of the present invention,spatial efficiency can be improved by performing dynamic CCA.Furthermore, a reduction of system throughput performance can beminimized due to an increase of spatial efficiency because the qualityand margin of a device which may be a victim in an interferenceenvironment are taken into consideration.

Furthermore, in accordance with an embodiment of the present invention,spatial reuse transmission can be applied to a longer time intervalbecause an OBSS STA performs dynamic CCA. Accordingly, frequency useefficiency can be further improved.

Furthermore, in accordance with an embodiment of the present invention,SR support information is generated based on SR indication informationdirectly generated by an AP, that is, a victim STA, by taking intoconsideration its own capabilities, a surrounding interferencesituation, and a channel situation. Accordingly, there is an advantagein that SR support information having the highest reliability istransmitted assuming that the same SR support information is transmittedto all of OBSS AP/STAs. Furthermore, if SR support information isgenerated identically with SR indication information, an STA cangenerate the SR support information by duplicating the SR indicationinformation received through a trigger frame without any change.Accordingly, there is an advantage in that a procedure for generating SRsupport information can become very simple.

Furthermore, in accordance with an embodiment of the present invention,SR indication information is signaled and transmitted in a trigger frame(MAC payload) that is transmitted in a broadcast manner. Accordingly,there is an advantage in that transmission overhead of SR indicationinformation is reduced because a plurality of STAs can receive the sameSR indication information at the same time.

Other advantages of the present invention are additionally described inthe following embodiments.

DESCRIPTION OF DRAWINGS

The accompany drawings, which are included to provide a furtherunderstanding of this document and are incorporated on and constitute apart of this specification illustrate embodiments of this document andtogether with the description serve to explain the principles of thisdocument.

FIG. 1 is a diagram showing an example of an IEEE 802.11 system to whichan embodiment of the present invention may be applied.

FIG. 2 is a diagram illustrating the configuration of layer architectureof an IEEE 802.11 system to which an embodiment of the present inventionmay be applied.

FIG. 3 illustrating a non-HT format PPDU and an HT format PPDU in awireless communication system to which an embodiment of the presentinvention may be applied.

FIG. 4 illustrates a VHT format PPDU in a wireless communication systemto which an embodiment of the present invention may be applied.

FIG. 5 is a diagram illustrating an HE format PPDU according to anembodiment of the present invention.

FIG. 6 is a diagram illustrating an HE format PPDU according to anembodiment of the present invention.

FIG. 7 is a diagram illustrating an HE format PPDU according to anembodiment of the present invention.

FIG. 8 is a conceptual diagram showing a method for performing CCAaccording to an embodiment of the present invention.

FIG. 9 is a flowchart illustrating a method for transmitting, by an STAapparatus, an UM MU PPDU according to an embodiment of the presentinvention.

FIG. 10 is a conceptual diagram showing a method for performing SRaccording to an embodiment of the present invention.

FIG. 11 is a diagram showing the structure of a trigger frame accordingto an embodiment of the present invention.

FIG. 12 is a block diagram of each STA apparatus according to anembodiment of the present invention.

MODE FOR INVENTION

Terms used in this specification are common terms now widely used bytaking into consideration functions in this specification, but the termsmay be changed depending on intentions of those skilled in the art, ause practice, or the appearance of a new technology. Furthermore, in aspecific case, some terms are randomly selected by the applicant. Inthis case, the detailed meaning of a corresponding term will bedescribed in the corresponding part of the description of thisspecification. Accordingly, the terms used in this specification shouldnot be interpreted simply based on their names, but should beinterpreted based on their substantial meanings and contents over thisspecification.

Furthermore, embodiments are described in detail with reference to theaccompanying drawings and contents described in the accompanyingdrawings, but the present invention is not limited to the embodiments.

Hereinafter, some embodiments of the present invention are described indetail with reference to the accompanying drawings.

The following technologies may be used in a variety of wirelesscommunication systems, such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), and non-orthogonalmultiple access (NOMA). CDMA may be implemented using a radiotechnology, such as universal terrestrial radio access (UTRA) orCDMA2000. TDMA may be implemented using a radio technology, such asglobal system for Mobile communications (GSM)/general packet radioservice (GPRS)/enhanced data rates for GSM evolution (EDGE). OFDMA maybe implemented using a radio technology, such as institute of electricaland electronics engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX),IEEE 802.20, or evolved UTRA (E-UTRA). UTRA is part of a universalmobile telecommunications system (UMTS). 3^(rd) generation partnershipproject (3GPP) long term evolution (LTE) is part of an evolved UMTS(E-UMTS) using evolved UMTS terrestrial radio access (E-UTRA), and itadopts OFDMA in downlink and adopts SC-FDMA in uplink. LTE-advanced(LTE-A) is the evolution of 3GPP LTE.

Embodiments of the present invention may be supported by the standarddocuments disclosed in at least one of IEEE 802, 3GPP, and 3GPP2, thatis, radio access systems. That is, steps or portions that belong to theembodiments of the present invention and that are not described in orderto clearly expose the technical spirit of the present invention may besupported by the documents. Furthermore, all terms disclosed in thisdocument may be described by the standard documents.

In order to more clarify a description, 3GPP LTE/LTE-A is chieflydescribed, but the technical characteristics of the present inventionare not limited thereto.

General System

FIG. 1 is a diagram showing an example of an IEEE 802.11 system to whichan embodiment of the present invention may be applied. In certainembodiments, the present invention is implemented in an IEEE 802.11 axnetwork environment.

The IEEE 802.11 configuration may include a plurality of elements. Theremay be provided a wireless communication system supporting transparentstation (STA) mobility for a higher layer through an interaction betweenthe elements. A basic service set (BSS) may correspond to a basicconfiguration block in an IEEE 802.11 system.

FIG. 1 illustrates that three BSSs BSS 1 to BSS 3 are present and twoSTAs (e.g., an STA 1 and an STA 2 are included in the BSS 1, an STA 3and an STA 4 are included in the BSS 2, and an STA 5 and an STA 6 areincluded in the BSS 3) are included as the members of each BSS.

In FIG. 1, an ellipse indicative of a BSS may be interpreted as beingindicative of a coverage area in which STAs included in thecorresponding BSS maintain communication. Such an area may be called abasic service area (BSA). When an STA moves outside the BSA, it isunable to directly communicate with other STAs within the correspondingBSA.

In the IEEE 802.11 system, the most basic type of a BSS is anindependent a BSS (IBSS). For example, an IBSS may have a minimum formincluding only two STAs. Furthermore, the BSS 3 of FIG. 1 which is thesimplest form and from which other elements have been omitted maycorrespond to a representative example of the IBSS. Such a configurationmay be possible if STAs can directly communicate with each other.Furthermore, a LAN of such a form is not previously planned andconfigured, but may be configured when it is necessary. This may also becalled an ad-hoc network.

When an STA is powered off or on or an STA enters into or exits from aBSS area, the membership of the STA in the BSS may be dynamicallychanged. In order to become a member of a BSS, an STA may join the BSSusing a synchronization process. In order to access all of services in aBSS-based configuration, an STA needs to be associated with the BSS.Such association may be dynamically configured, and may include the useof a distribution system service (DSS).

In an 802.11 system, the distance of a direct STA-to-STA may beconstrained by physical layer (PHY) performance. In any case, the limitof such a distance may be sufficient, but communication between STAs ina longer distance may be required, if necessary. In order to supportextended coverage, a distribution system (DS) may be configured.

The DS means a configuration in which BSSs are interconnected. Morespecifically, a BSS may be present as an element of an extended form ofa network including a plurality of BSSs instead of an independent BSS asin FIG. 1.

The DS is a logical concept and may be specified by the characteristicsof a distribution system medium (DSM). In the IEEE 802.11 standard, awireless medium (WM) and a distribution system medium (DSM) arelogically divided. Each logical medium is used for a different purposeand used by a different element. In the definition of the IEEE 802.11standard, such media are not limited to the same one and are also notlimited to different ones. The flexibility of the configuration (i.e., aDS configuration or another network configuration) of an IEEE 802.11system may be described in that a plurality of media is logicallydifferent as described above. That is, an IEEE 802.11 systemconfiguration may be implemented in various ways, and a correspondingsystem configuration may be independently specified by the physicalcharacteristics of each implementation example.

The DS can support a mobile device by providing the seamless integrationof a plurality of BSSs and providing logical services required to handlean address to a destination.

An AP means an entity which enables access to a DS through a WM withrespect to associated STAs and has the STA functionality. The movementof data between a BSS and the DS can be performed through an AP. Forexample, each of the STA 2 and the STA 3 of FIG. 1 has the functionalityof an STA and provides a function which enables associated STAs (e.g.,the STA 1 and the STA 4) to access the DS. Furthermore, all of APsbasically correspond to an STA, and thus all of the APs are entitiescapable of being addressed. An address used by an AP for communicationon a WM and an address used by an AP for communication on a DSM may notneed to be necessarily the same.

Data transmitted from one of STAs, associated with an AP, to the STAaddress of the AP may be always received by an uncontrolled port andprocessed by an IEEE 802.1X port access entity. Furthermore, when acontrolled port is authenticated, transmission data (or frame) may bedelivered to a DS.

A wireless network having an arbitrary size and complexity may include aDS and BSSs. In an IEEE 802.11 system, a network of such a method iscalled an extended service set (ESS) network. The ESS may correspond toa set of BSSs connected to a single DS. However, the ESS does notinclude a DS. The ESS network is characterized in that it looks like anIBSS network in a logical link control (LLC) layer. STAs included in theESS may communicate with each other. Mobile STAs may move from one BSSto the other BSS (within the same ESS) in a manner transparent to theLLC layer.

In an IEEE 802.11 system, the relative physical positions of BSSs inFIG. 1 are not assumed, and the following forms are all possible.

More specifically, BSSs may partially overlap, which is a form commonlyused to provide consecutive coverage. Furthermore, BSSs may not bephysically connected, and logically there is no limit to the distancebetween BSSs. Furthermore, BSSs may be placed in the same positionphysically and may be used to provide redundancy. Furthermore, one (orone or more) IBSS or ESS networks may be physically present in the samespace as one or more ESS networks. This may correspond to an ESS networkform if an ad-hoc network operates at the position in which an ESSnetwork is present, if IEEE 802.11 networks that physically overlap areconfigured by different organizations, or if two or more differentaccess and security policies are required at the same position.

In a WLAN system, an STA is an apparatus operating in accordance withthe medium access control (MAC)/PHY regulations of IEEE 802.11. An STAmay include an AP STA and a non-AP STA unless the functionality of theSTA is not individually different from that of an AP. In this case,assuming that communication is performed between an STA and an AP, theSTA may be interpreted as being a non-AP STA. In the example of FIG. 1,the STA 1, the STA 4, the STA 5, and the STA 6 correspond to non-APSTAs, and the STA 2 and the STA 3 correspond to AP STAs.

A non-AP STA corresponds to an apparatus directly handled by a user,such as a laptop computer or a mobile phone. In the followingdescription, a non-AP STA may also be called a wireless device, aterminal, user equipment (UE), a mobile station (MS), a mobile terminal,a wireless terminal, a wireless transmit/receive unit (WTRU), a networkinterface device, a machine-type communication (MTC) device, amachine-to-machine (M2M) device or the like.

Furthermore, an AP is a concept corresponding to a base station (BS), anode-B, an evolved Node-B (eNB), a base transceiver system (BTS), afemto BS or the like in other wireless communication fields.

Hereinafter, in this specification, downlink (DL) means communicationfrom an AP to a non-AP STA. Uplink (UL) means communication from anon-AP STA to an AP. In DL, a transmitter may be part of an AP, and areceiver may be part of a non-AP STA. In UL, a transmitter may be partof a non-AP STA, and a receiver may be part of an AP.

FIG. 2 is a diagram illustrating the configuration of layer architectureof an IEEE 802.11 system to which an embodiment of the present inventionmay be applied.

Referring to FIG. 2, the layer architecture of the IEEE 802.11 systemmay include an MAC sublayer and a PHY sublayer.

The PHY sublayer may be divided into a physical layer convergenceprocedure (PLCP) entity and a physical medium dependent (PMD) entity. Inthis case, the PLCP entity functions to connect the MAC sublayer and adata frame, and the PMD entity functions to wirelessly transmit andreceive data to and from two or more STAs.

The MAC sublayer and the PHY sublayer may include respective managemententities, which may be referred to as an MAC sublayer management entity(MLME) and a PHY sublayer management entity (PLME), respectively. Themanagement entities provide a layer management service interface throughthe operation of a layer management function. The MLME is connected tothe PLME and may perform the management operation of the MAC sublayer.Likewise, the PLME is also connected to the MLME and may perform themanagement operation of the PHY sublayer.

In order to provide a precise MAC operation, a station management entity(SME) may be present in each STA. The SME is a management entityindependent of each layer, and collects layer-based state informationfrom the MLME and the PLME or sets the values of layer-specificparameters. The SME may perform such a function instead of common systemmanagement entities and may implement a standard management protocol.

The MLME, the PLME, and the SME may interact with each other usingvarious methods based on primitives. More specifically, anXX-GET.request primitive is used to request the value of a managementinformation base (MIB) attribute. An XX-GET.confirm primitive returnsthe value of a corresponding MIB attribute if the state is “SUCCESS”,and indicates an error in the state field and returns the value in othercases. An XX-SET.request primitive is used to make a request so that adesignated MIB attribute is set as a given value. If an MIB attributemeans a specific operation, such a request requests the execution of thespecific operation. Furthermore, an XX-SET.confirm primitive means thata designated MIB attribute has been set as a requested value if thestate is “SUCCESS.” In other cases, the XX-SET.confirm primitiveindicates that the state field is an error situation. If an MIBattribute means a specific operation, the primitive may confirm that acorresponding operation has been performed.

An operation in each sublayer is described in brief as follows.

The MAC sublayer generates one or more MAC protocol data units (MPDUs)by attaching an MAC header and a frame check sequence (FCS) to a MACservice data unit (MSDU) received from a higher layer (e.g., an LLClayer) or the fragment of the MSDU. The generated MPDU is delivered tothe PHY sublayer.

If an aggregated MSDU (A-MSDU) scheme is used, a plurality of MSDUs maybe aggregated into a single aggregated MSDU (A-MSDU). The MSDUaggregation operation may be performed in an MAC higher layer. TheA-MSDU is delivered to the PHY sublayer as a single MPDU (if it is notfragmented).

The PHY sublayer generates a physical protocol data unit (PPDU) byattaching an additional field, including information for a PHYtransceiver, to a physical service data unit (PSDU) received from theMAC sublayer. The PPDU is transmitted through a wireless medium.

The PSDU has been received by the PHY sublayer from the MAC sublayer,and the MPDU has been transmitted from the MAC sublayer to the PHYsublayer. Accordingly, the PSDU is substantially the same as the MPDU.

If an aggregated MPDU (A-MPDU) scheme is used, a plurality of MPDUs (inthis case, each MPDU may carry an A-MSDU) may be aggregated in a singleA-MPDU. The MPDU aggregation operation may be performed in an MAC lowerlayer. The A-MPDU may include an aggregation of various types of MPDUs(e.g., QoS data, acknowledge (ACK), and a block ACK (BlockAck)). The PHYsublayer receives an A-MPDU, that is, a single PSDU, from the MACsublayer. That is, the PSDU includes a plurality of MPDUs. Accordingly,the A-MPDU is transmitted through a wireless medium within a singlePPDU.

Physical Protocol Data Unit (PPDU) Format

A PPDU means a data block generated in the physical layer. A PPDU formatis described below based on an IEEE 802.11 a WLAN system to which anembodiment of the present invention may be applied.

FIG. 3 illustrating a non-HT format PPDU and an HT format PPDU in awireless communication system to which an embodiment of the presentinvention may be applied.

FIG. 3(a) illustrates a non-HT format PPDU for supporting IEEE 802.11a/gsystems. The non-HT PPDU may also be called a legacy PPDU.

Referring to FIG. 3(a), the non-HT format PPDU is configured to includea legacy format preamble, including a legacy (or non-HT) short trainingfield (L-STF), a legacy (or non-HT) long training field (L-LTF), and alegacy (or non-HT) signal (L-SIG) field, and a data field.

The L-STF may include a short training orthogonal frequency divisionmultiplexing symbol (OFDM). The L-STF may be used for frame timingacquisition, automatic gain control (AGC), diversity detection, andcoarse frequency/time synchronization.

The L-LTF may include a long training OFDM symbol. The L-LTF may be usedfor fine frequency/time synchronization and channel estimation.

The L-SIG field may be used to send control information for thedemodulation and decoding of the data field.

The L-SIG field may include a rate (Rate) field of 4 bits, a reservedbit of 1 bit, a length (Length) field of 12 bits, a parity bit of 1 bit,and a signal tail field of 6 bits.

The rate field includes transfer rate information, and the length fieldindicates the number of octets of a PSDU.

FIG. 3(b) illustrates an HT mixed format PPDU for supporting both anIEEE 802.11n system and IEEE 802.11a/g system.

Referring to FIG. 3(b), the HT mixed format PPDU is configured toinclude a legacy format preamble including an L-STF, an L-LTF, and anL-SIG field, an HT format preamble including an HT-signal (HT-SIG)field, a HT short training field (HT-STF), and a HT long training field(HT-LTF), and a data field.

The L-STF, the L-LTF, and the L-SIG field mean legacy fields forbackward compatibility and are the same as those of the non-HT formatfrom the L-STF to the L-SIG field. An L-STA may interpret a data fieldthrough an L-LTF, an L-LTF, and an L-SIG field although it receives anHT mixed PPDU. In this case, the L-LTF may further include informationfor channel estimation to be performed by an HT-STA in order to receivethe HT mixed PPDU and to demodulate the L-SIG field and the HT-SIGfield.

An HT-STA may be aware of an HT mixed format PPDU using the HT-SIG fieldsubsequent to the legacy fields, and may decode the data field based onthe HT mixed format PPDU.

The HT-LTF may be used for channel estimation for the demodulation ofthe data field. IEEE 802.11n supports single user multi-input andmulti-output (SU-MIMO) and thus may include a plurality of HT-LTFs forchannel estimation with respect to each of data fields transmitted in aplurality of spatial streams.

The HT-LTF may include a data HT-LTF used for channel estimation for aspatial stream and an extension HT-LTF additionally used for fullchannel sounding. Accordingly, a plurality of HT-LTFs may be the same asor greater than the number of transmitted spatial streams.

In the HT mixed format PPDU, the L-STF, the L-LTF, and the L-SIG fieldsare first transmitted so that an L-STA can receive the L-STF, the L-LTF,and the L-SIG fields and obtain data. Thereafter, the HT-SIG field istransmitted for the demodulation and decoding of data transmitted for anHT-STA.

An L-STF, an L-LTF, and L-SIG fields are transmitted without performingbeamforming up to an HT-SIG field so that an L-STA and an HT-STA canreceive a corresponding PPDU and obtain data. In an HT-STF, an HT-LTF,and a data field that are subsequently transmitted, radio signals aretransmitted through precoding. In this case, an HT-STF is transmitted sothat an STA receiving a corresponding PPDU by performing precoding maytake into considerate a portion whose power is varied by precoding, anda plurality of HT-LTFs and a data field are subsequently transmitted.

Table 1 below is a table showing the HT-SIG field.

TABLE 1 FIELD BIT DESCRIPTION MCS 7 Indicate a modulation and codingscheme CBW 20/40 1 Set to “0” if a CBW is 20 MHz or 40 MHz orupper/lower Set to “1” if a CBW is 40 MHz HT length 16 Indicate thenumber of data octets within a PSDU Smoothing 1 Set to “1” if channelsmoothing is recommended Set to “0” if channel estimation is recommendedunsmoothingly for each carrier Not-sounding 1 Set to “0” if a PPDU is asounding PPDU Set to “1” if a PPDU is not a sounding PPDU Reserved 1 Setto “1” Aggregation 1 Set to “1” if a PPDU includes an A-MPDU Set to “0”if not Space-time 2 Indicate a difference between the number ofspace-time streams (NSTS) block coding and the number of spatial streams(NSS) indicated by an MCS (STBC) Set to “00” if an STBC is not used FECcoding 1 Set to “1” if low-density parity check (LDPC) is used Set to“0” if binary convolutional code (BCC) is used Short GI 1 Set to “1” ifa short guard interval (GI) is used after HT training Set to “0” if notNumber of 2 Indicate the number of extension spatial streams (NESSs)extension Set to “0” if there is no NESS spatial streams Set to “1” ifthe number of NESSs is 1 Set to “2” if the number of NESSs is 2 Set to“3” if the number of NESSs is 3 CRC 8 Include CRS for detecting an errorof a PPDU on the receiver side Tail bits 6 Used to terminate the trellisof a convolutional decoder Set to “0”

FIG. 3(c) illustrates an HT-green field format PPDU (HT-GF format PPDU)for supporting only an IEEE 802.11n system.

Referring to FIG. 3(c), the HT-GF format PPDU includes an HT-GF-STF, anHT-LTF1, an HT-SIG field, a plurality of HT-LTF2s, and a data field.

The HT-GF-STF is used for frame timing acquisition and AGC.

The HT-LTF1 is used for channel estimation.

The HT-SIG field is used for the demodulation and decoding of the datafield.

The HT-LTF2 is used for channel estimation for the demodulation of thedata field. Likewise, an HT-STA uses SU-MIMO. Accordingly, a pluralityof the HT-LTF2s may be configured because channel estimation isnecessary for each of data fields transmitted in a plurality of spatialstreams.

The plurality of HT-LTF2s may include a plurality of data HT-LTFs and aplurality of extension HT-LTFs like the HT-LTF of the HT mixed PPDU.

In FIGS. 3(a) to 3(c), the data field is a payload and may include aservice field, a scrambled PSDU (PSDU) field, tail bits, and paddingbits. All of the bits of the data field are scrambled.

FIG. 3(d) illustrates a service field included in the data field. Theservice field has 16 bits. The 16 bits are assigned No. 0 to No. 15 andare sequentially transmitted from the No. 0 bit. The No. 0 bit to theNo. 6 bit are set to 0 and are used to synchronize a descrambler withina reception stage.

An IEEE 802.11ac WLAN system supports the transmission of a DLmulti-user multiple input multiple output (MU-MIMO) method in which aplurality of STAs accesses a channel at the same time in order toefficiently use a radio channel. In accordance with the MU-MIMOtransmission method, an AP may simultaneously transmit a packet to oneor more STAs that have been subjected to MIMO pairing.

Downlink multi-user transmission (DL MU transmission) means a technologyin which an AP transmits a PPDU to a plurality of non-AP STAs throughthe same time resources using one or more antennas.

Hereinafter, an MU PPDU means a PPDU which delivers one or more PSDUsfor one or more STAs using the MU-MIMO technology or the OFDMAtechnology.

Furthermore, an SU PPDU means a PPDU having a format in which only onePSDU can be delivered or which does not have a PSDU.

For MU-MIMO transmission, the size of control information transmitted toan STA may be relatively larger than the size of 802.11n controlinformation. Control information additionally required to supportMU-MIMO may include information indicating the number of spatial streamsreceived by each STA and information related to the modulation andcoding of data transmitted to each STA may correspond to the controlinformation, for example.

Accordingly, when MU-MIMO transmission is performed to provide aplurality of STAs with a data service at the same time, the size oftransmitted control information may be increased according to the numberof STAs which receive the control information.

In order to efficiently transmit the control information whose size isincreased as described above, a plurality of pieces of controlinformation required for MU-MIMO transmission may be divided into twotypes of control information: common control information that isrequired for all of STAs in common and dedicated control informationindividually required for a specific STA, and may be transmitted.

FIG. 4 illustrates a VHT format PPDU in a wireless communication systemto which an embodiment of the present invention may be applied.

FIG. 4(a) illustrates a VHT format PPDU for supporting an IEEE 802.11acsystem.

Referring to FIG. 4(a), the VHT format PPDU is configured to include alegacy format preamble including an L-STF, an L-LTF, and an L-SIG field,a VHT format preamble including a VHT-signal-A (VHT-SIG-A) field, a VHTshort training field (VHT-STF), a VHT long training field (VHT-LTF), anda VHT-signal-B (VHT-SIG-B) field, and a data field.

The L-STF, the L-LTF, and the L-SIG field mean legacy fields forbackward compatibility and have the same formats as those of the non-HTformat. In this case, the L-LTF may further include information forchannel estimation which will be performed in order to demodulate theL-SIG field and the VHT-SIG-A field.

The L-STF, the L-LTF, the L-SIG field, and the VHT-SIG-A field may berepeated in a 20 MHz channel unit and transmitted. For example, when aPPDU is transmitted through four 20 MHz channels (i.e., an 80 MHzbandwidth), the L-STF, the L-LTF, the L-SIG field, and the VHT-SIG-Afield may be repeated every 20 MHz channel and transmitted.

A VHT-STA may be aware of the VHT format PPDU using the VHT-SIG-A fieldsubsequent to the legacy fields, and may decode the data field based onthe VHT-SIG-A field.

In the VHT format PPDU, the L-STF, the L-LTF, and the L-SIG field arefirst transmitted so that even an L-STA can receive the VHT format PPDUand obtain data. Thereafter, the VHT-SIG-A field is transmitted for thedemodulation and decoding of data transmitted for a VHT-STA.

The VHT-SIG-A field is a field for the transmission of controlinformation that is common to a VHT STAs that are MIMO-paired with anAP, and includes control information for interpreting the received VHTformat PPDU.

The VHT-SIG-A field may include a VHT-SIG-A1 field and a VHT-SIG-A2field.

The VHT-SIG-A1 field may include information about a channel bandwidth(BW) used, information about whether space time block coding (STBC) isapplied or not, a group identifier (ID) for indicating a group ofgrouped STAs in MU-MIMO, information about the number of streams used(the number of space-time streams (NSTS)/part association identifier(AID), and transmit power save forbidden information. In this case, thegroup ID means an identifier assigned to a target transmission STA groupin order to support MU-MIMO transmission, and may indicate whether thepresent MIMO transmission method is MU-MIMO or SU-MIMO.

Table 2 is a table showing the VHT-SIG-A1 field.

TABLE 2 FIELD BIT DESCRIPTION BW 2 Set to “0” if a BW is 20 MHz Set to“1” if a BW is 40 MHz Set to “2” if a BW is 80 MHz Set to “3” if a BW is160 MHz or 80 + 80 MHz Reserved 1 STBC 1 In the case of a VHT SU PPDU:Set to “1” if STBC is used Set to “0” if not In the case of a VHT MUPPDU: Set to “0” group ID 6 Indicate a group ID “0” or “63” indicates aVHT SU PPDU, but indicates a VHT MU PPDU if not NSTS/Partial 12 In thecase of a VHT MU PPDU, divide into 4 user positions “p” each AID havingthree bits “0” if a space-time stream is 0 “1” if a space-time stream is1 “2” if a space-time stream is 2 “3” if a space-time stream is 3 “4” ifa space-time stream is 4 In the case of a VHT SU PPDU, Upper 3 bits areset as follows: “0” if a space-time stream is 1 “1” if a space-timestream is 2 “2” if a space-time stream is 3 “3” if a space-time streamis 4 “4” if a space-time stream is 5 “5” if a space-time stream is 6 “6”if a space-time stream is 7 “7” if a space-time stream is 8 Lower 9 bitsindicate a partial AID. TX0P_PS_NOT_ALLOWED 1 Set to “0” if a VHT APpermits a non-AP VHT STA to switch to power save mode duringtransmission opportunity (TXOP) Set to “1” if not In the case of a VHTPPDU transmitted by a non-AP VHT STA Set to “1” Reserved 1

The VHT-SIG-A2 field may include information about whether a short guardinterval (GI) is used or not, forward error correction (FEC)information, information about a modulation and coding scheme (MCS) fora single user, information about the type of channel coding for multipleusers, beamforming-related information, redundancy bits for cyclicredundancy checking (CRC), the tail bits of a convolutional decoder andso on.

Table 3 is a table showing the VHT-SIG-A2 field.

TABLE 3 FIELD BIT DESCRIPTION Short GI 1 Set to “0” if a short GI is notused in a data field Set to “1” if a short GI is used in a data fieldShort GI 1 Set to “1” if a short GI is used and an extra symbol isrequired for the disambiguation payload of a PPDU Set to “0” if an extrasymbol is not required SU/MU coding 1 In the case of a VHT SU PPDU: Setto “0” in the case of binary convolutional code (BCC) Set to “1” in thecase of low-density parity check (LDPC) In the case of a VHT MU PPDU:Indicate coding used if the NSTS field of a user whose user position is“0” is not “0” Set to “0” in the case of BCC Set to “1” in the case ofPDPC Set to “1” as a reserved field if the NSTS field of a user whoseuser position is “0” is “0” LDPC Extra 1 Set to “1” if an extra OFDMsymbol is required due to an PDPC OFDM symbol PPDU encoding procedure(in the case of a SU PPDU) or the PPDU encoding procedure of at leastone PDPC user (in the case of a VHT MU PPDU) Set to “0” if not SU VHTMCS/MU 4 In the case of a VHT SU PPDU: coding Indicate a VHT-MCS indexIn the case of a VHT MU PPDU: Indicate coding for user positions “1” to“3” sequentially from upper bits Indicate coding used if the NSTS fieldof each user is not “1” Set to “0” in the case of BCC Set to “1” in thecase of LDPC Set to “1” as a reserved field if the NSTS field of eachuser is “0” Beamformed 1 In the case of a VHT SU PPDU: Set to “1” if abeamforming steering matrix is applied to SU transmission Set to “0” ifnot In the case of a VHT MU PPDU: Set to “1” as a reserved fieldReserved 1 CRC 8 Include CRS for detecting an error of a PPDU on thereceiver side Tail 6 Used to terminate the trellis of a convolutionaldecoder Set to “0”

The VHT-STF is used to improve AGC estimation performance in MIMOtransmission.

The VHT-LTF is used for a VHT-STA to estimate an MIMO channel Since aVHT WLAN system supports MU-MIMO, the VHT-LTF may be configured by thenumber of spatial streams through which a PPDU is transmitted.Additionally, if full channel sounding is supported, the number ofVHT-LTFs may be increased.

The VHT-SIG-B field includes dedicated control information which isnecessary for a plurality of MU-MIMO-paired VHT-STAs to receive a PPDUand to obtain data. Accordingly, only when common control informationincluded in the VHT-SIG-A field indicates that a received PPDU is forMU-MIMO transmission, a VHT-STA may be designed to decode the VHT-SIG-Bfield. In contrast, if common control information indicates that areceived PPDU is for a single VHT-STA (including SU-MIMO), an STA may bedesigned to not decode the VHT-SIG-B field.

The VHT-SIG-B field includes a VHT-SIG-B length field, a VHT-MCS field,a reserved field, and a tail field.

The VHT-SIG-B length (Length) field indicates the length (prior to thepadding of an end-of-frame (EOF)) of an A-MPDU. The VHT-MCS fieldincludes information about the modulation, encoding, and rate-matchingof each VHT-STA.

The size of the VHT-SIG-B field may be different depending on the type(MU-MIMO or SU-MIMO) of MIMO transmission and a channel bandwidth usedfor PPDU transmission.

FIG. 4(b) illustrates a VHT-SIG-B field according to a PPDU transmissionbandwidth.

Referring to FIG. 4(b), in 40 MHz transmission, the bits of theVHT-SIG-B field are repeated twice. In 80 MHz transmission, the bits ofthe VHT-SIG-B field are repeated four times, and pad bits set to 0 areattached to the VHT-SIG-B field.

In 160 MHz transmission and 80+80 MHz transmission, first, the bits ofthe VHT-SIG-B field are repeated four times and pad bits set to 0 areattached to the VHT-SIG-B field as in 80 MHz transmission. Furthermore,all of the 117 bits are repeated again.

In a system supporting MU-MIMO, in order to transmit PPDUs having thesame size to STAs paired with an AP, information indicating the size ofthe bits of a data field forming the PPDU and/or information indicatingthe size of bit streams forming a specific field may be included in theVHT-SIG-A field.

In this case, an L-SIG field may be used to effectively use a PPDUformat. A length field and a rate field which are included in the L-SIGfield and transmitted so that PPDUs having the same size are transmittedto all of STAs may be used to provide required information. In thiscase, additional padding may be required in the physical layer becausean MAC protocol data unit (MPDU) and/or an aggregate MAC PDU (A-MPDU)are set based on the bytes (or octets) of the MAC layer.

In FIG. 4, the data field is a payload and may include a service field,a scrambled PSDU, tail bits, and padding bits.

An STA needs to determine the format of a received PPDU because severalformats of PPDUs are mixed and used as described above.

In this case, the meaning that a PPDU (or a PPDU format) is determinedmay be various. For example, the meaning that a PPDU is determined mayinclude determining whether a received PPDU is a PPDU capable of beingdecoded (or interpreted) by an STA. Furthermore, the meaning that a PPDUis determined may include determining whether a received PPDU is a PPDUcapable of being supported by an STA. Furthermore, the meaning that aPPDU is determined may include determining that information transmittedthrough a received PPDU is which information.

This is described in more detail with reference to FIG. 5.

UL MU Transmission Method

Many vendors of various fields have a lot of interest in thenext-generation Wi-Fi, and there is a growing demand for the improvementof high throughput and quality of experience (QoE) performance after802.11ac. Accordingly, a new frame format and numerology for an 802.11axsystem, that is, the next-generation WLAN system, are activelydiscussed.

IEEE 802.11ax is one of recently proposed WLAN systems as thenext-generation WLAN system for supporting a higher data rate andprocessing a higher user load, and is also called a so-called highefficiency WLAN (HEW).

The IEEE 802.11ax WLAN system may operate in a 2.4 GHz frequency bandand a 5 GHz frequency band like the existing WLAN system. Furthermore,the IEEE 802.11ax WLAN system may also operate in a higher 60 GHzfrequency band.

In the IEEE 802.11ax system, an FFT size that is four times greater ineach bandwidth than that of the existing IEEE 802.11 OFDM systems (e.g.,IEEE 802.11a, 802.11n, and 802.11ac) may be used for average throughputenhancement and outdoor robust transmission for inter-symbolinterference in outdoor environments. This is described below withreference to related drawings.

In the following description of an HE format PPDU, the aforementioneddescriptions of the non-HT format PPDU, the HT-mixed format PPDU, theHT-green field format PPDU and/or the VHT format PPDU may be merged withthe description of the HE format PPDU unless described otherwise.Furthermore, the HE format PPDU may include a physical (PHY) preambleand a data field. The PHY preamble may include an HE-SIG A field, anHE-SIG B field, an HE-STF and/or an HE-LTF in addition to theaforementioned L-STF, L-LTF, and L-SIG field. The HE format fields aredescribed in detail later with reference to related drawings.

FIG. 5 is a diagram illustrating an HE format PPDU according to anembodiment of the present invention.

FIG. 5 shows an example of an PPDU format in which 80 MHz is allocatedto a single STA (or if an OFDMA resource unit is allocated to aplurality of STAs within 80 MHz) or different streams of 80 MHz arerespectively allocated to a plurality of STAs.

Referring to FIG. 5, an L-STF, an L-LTF, and an L-SIG field may betransmitted in an OFDM symbol generated based on 64 FFT points (or 64subcarriers) in each 20 MHz channel.

Furthermore, an HE-SIG B field may be placed subsequent to an HE-SIG Afield. In this case, an FFT size per unit frequency may be furtherincreased after an HE-STF (or the HE-SIG B field). For example, from theHE-STF (or the HE-SIG B field), 256 FFT may be used in a 20 MHz channel,512 FFT may be used in a 40 MHz channel, and 1024 FFT may be used in an80 MHz channel.

The HE-SIG A field may include common control information (i.e., acommon field) in common transmitted to STAs that receive a PPDU. TheHE-SIG A field may be transmitted in one or three OFDM symbols. TheHE-SIG A field is duplicated in a 20 MHz unit and includes the sameinformation. Furthermore, the HE-SIG A field provides notification ofthe entire bandwidth information of a system.

Table 4 is a table showing information included in the HE-SIG A field.

TABLE 4 FIELD BIT DESCRIPTION Bandwidth 2 Indicate a bandwidth in whicha PPDU is transmitted, for example, 20 MHz, 40 MHz, 80 MHz, or 160 MHzGroup ID 6 Indicate an STA or a group of STAs which will receive a PPDUStream 12 Indicate the location or number of a spatial stream for eachSTA or information indicate the location or number of a spatial streamfor a group of STAs UL indication 1 Indicate whether a PPDU is directedto an AP (i.e., uplink) or is directed to an STA (i.e., downlink) MUindication 1 Indicate whether a PPDU is an SU-MIMO PPDU or MU-MIMO PPDUGI indication 1 Indicate whether a short GI or a long GI is usedAllocation 12 Indicate a band or channel (or a subchannel index or asubband index) information allocated to each STA in a band in which aPPDU is transmitted Transmission 12 Indicate transmission power for eachchannel or each STA power

The information included in each of the fields illustrated in Table 4may comply with the definition of the IEEE 802.11 system. Furthermore,the aforementioned fields correspond to an example of fields which maybe included in a PPDU, but the present invention is not limited thereto.That is, the fields may be substituted with different fields or mayfurther include an additional field. All of the fields may not beessentially included. Another embodiment of information included in theHE-SIG A field is described later with reference to FIG. 6.

The HE-STF is used to improve AGC estimation performance in MIMOtransmission.

The HE-SIG B field may include user-specific information that isrequired for each STA to receive its own data (e.g., a PSDU). The HE-SIGB field may be transmitted in one or two OFDM symbols. For example, theHE-SIG B field may include information about the modulation and codingscheme (MCS) of a corresponding PSDU and the length of the correspondingPSDU.

The L-STF, L-LTF, L-SIG field, and HE-SIG A field may be repeated in a20 MHz channel unit and transmitted. For example, when a PPDU istransmitted through four 20 MHz channels (i.e., a 80 MHz band), theL-STF, L-LTF, L-SIG field, and HE-SIG A field may be repeated every 20MHz channel and transmitted.

If an FFT size is increased, a legacy STA supporting the existing IEEE802.11a/g/n/ac systems may not decode a corresponding HE PPDU. In orderfor a legacy STA and an HE STA to coexist, the L-STF, L-LTF, and L-SIGfield are transmitted through 64 FFT in a 20 MHz channel so that thelegacy STA may receive a corresponding HE PPDU. For example, the L-SIGfield may occupy a single OFDM symbol, the single OFDM symbol time maybe 4 μs, and a GI may be 0.8 μs.

An FFT size for each frequency unit may be further increased from theHE-STF (or the HE-SIG A field). For example, 256 FFT may be used in a 20MHz channel, 512 FFT may be used in a 40 MHz channel, and 1024 FFT maybe used in an 80 MHz channel. If the FFT size increases, the number ofOFDM subcarriers per unit frequency increases because spacing betweenOFDM subcarriers is reduced, but an OFDM symbol time increases. In orderto improve system efficiency, the length of a GI after the HE-STF may beconfigured to be the same as the length of the GI of the HE-SIG A field.

The HE-SIG A field may include information that is required for an HESTA to decode a corresponding HE PPDU. However, the HE-SIG A field maybe transmitted through 64 FFT in a 20 MHz channel so that both a legacySTA and an HE STA may receive a corresponding HE PPDU. The reason forthis is that the HE STA has to receive an existing HT/VHT format PPDU inaddition to the HE format PPDU and the legacy STA and the HE STA have todistinguish the HT/VHT format PPDU from the HE format PPDU.

FIG. 6 is a diagram illustrating an HE format PPDU according to anembodiment of the present invention.

FIG. 6 shows an example in which 20 MHz channels are allocated todifferent STAs (e.g., an STA 1, an STA 2, an STA 3, and an STA 4).

Referring to FIG. 6, an FFT size per unit frequency may further increasefrom an HE-STF (or an HE-SIG B field). For example, from the HE-STF (orthe HE-SIG B field), 256 FFT may be used in a 20 MHz channel, 512 FFTmay be used in a 40 MHz channel, and 1024 FFT may be used in an 80 MHzchannel.

Information transmitted in each field included in a PPDU is the same asthat of FIG. 26, and a description thereof is omitted.

The HE-SIG B field may include information specific to each STA, but maybe encoded over the entire band (i.e., indicated in an HE-SIG A field).That is, the HE-SIG B field includes information about all of STAs, andis received by all of the STAs.

The HE-SIG B field may provide notification of information about afrequency bandwidth allocated to each STA and/or stream information in acorresponding frequency band. For example, in FIG. 6, in the HE-SIG Bfield, 20 MHz may be allocated to the STA 1, subsequent 20 MHz may beallocated to the STA 2, subsequent 20 MHz may be allocated to the STA 3,and subsequent 20 MHz may be allocated to the STA 4. In an embodiment,40 MHz may be allocated to the STA 1 and the STA 2, and 40 MHz may beallocated to the STA 3 and the STA 4. In this case, different streamsmay be allocated to the STA 1 and the STA 2, and different streams maybe allocated to the STA 3 and the STA 4.

Furthermore, an HE-SIG-C field may be defined and added to the exampleof FIG. 6. In this case, information about all of STAs may betransmitted over the entire band in the HE-SIG B field, and controlinformation specific to each STA may be transmitted in a 20 MHz unitthrough the HE-SIG-C field.

Furthermore, unlike in the examples of FIGS. 5 and 6, the HE-SIG B fieldis not transmitted over the entire band, but may be transmitted in a 20MHz unit like the HE-SIG A field. This is described below with referenceto FIG. 7.

FIG. 7 is a diagram illustrating an HE format PPDU according to anembodiment of the present invention.

FIG. 7 shows an example in which 20 MHz channels are allocated todifferent STAs (e.g., an STA 1, an STA 2, an STA 3, and an STA 4).

Referring to FIG. 7, an HE-SIG B field is not transmitted over theentire band, but is transmitted in a 20 MHz unit like an HE-SIG A field.In this case, the HE-SIG B field is encoded in a 20 MHz unit unlike theHE-SIG A field, but may be duplicated in a 20 MHz unit and may not betransmitted.

In this case, an FFT size per unit frequency may further increase froman HE-STF (or the HE-SIG B field). For example, from the HE-STF (or theHE-SIG B field), 256 FFT may be used in a 20 MHz channel, 512 FFT may beused in a 40 MHz channel, and 1024 FFT may be used in an 80 MHz channel.

Information transmitted in each field included in a corresponding PPDUis the same as that of FIG. 26, and a description thereof is omitted.

The HE-SIG A field is duplicated in a 20 MHz unit and transmitted.

The HE-SIG B field may provide notification of information about afrequency bandwidth allocated to each STA and/or stream information in acorresponding frequency band. Since the HE-SIG B field includesinformation about each STA, it may include information about each STA ina 20 MHz unit. In this case, FIG. 7 shows an example in which 20 MHz isallocated to each STA. For example, if 40 MHz is allocated to each STA,the HE-SIG B field may be duplicated in a 20 MHz unit and transmitted.

In a situation in which a different bandwidth is supported for each BSS,if some bandwidth having a low interference level from a neighboring BSSis allocated to an STA, it may be preferred that the HE-SIG B field isnot transmitted over the entire band as described above.

For example, the HE format PPDU of FIG. 7 is described below, forconvenience of description.

In FIGS. 5 to 7, a data field is payload and may include a servicefield, a scrambled PSDU, tail bits, and padding bits.

HE format PPDUs, such as those of FIGS. 5 to 7, may be identified basedon a repeated L-SIG (RL-SIG) field, that is, a repetition symbol of theL-SIG field. The RL-SIG field is inserted prior to the HE SIG-A field,and each STA may determine the format of a received PPDU to be an HEformat PPDU using the RL-SIG field.

A method in which an AP operating in a WLAN system transmits data to aplurality of STAs on the same time resource may be called downlinkmulti-user (DL MU) transmission. In contrast, a method in which aplurality of STAs operating in a WLAN system transmits data to an AP onthe same time resource may be called uplink multi-user (UL MU)transmission.

Hereinafter, DL MU transmission or UL MU transmission may be multiplexedon a frequency domain or a spatial domain.

If DL MU transmission or UL MU transmission is multiplexed on thefrequency domain, different frequency resources (e.g., subcarriers ortones) may be allocated to a plurality of STAs as DL or UL resourcesbased on orthogonal frequency division multiplexing (OFDMA). Such atransmission method through different frequency resources on the sametime resource may be referred to as “DL/UL MU OFDMA transmission.”

If DL MU transmission or UL MU transmission is multiplexed on thespatial domain, different spatial streams may be allocated to aplurality of STAs as DL or UL resources. Such a transmission methodthrough different spatial streams on the same time resources may bereferred to as “DL/UL MU MIMO transmission.”

The current WLAN system does not support UL MU transmission due to thefollowing constraints.

In the current WLAN system, synchronization for transmission timing ofUL data transmitted by a plurality of STAs is not supported. Forexample, assuming that a plurality of STAs transmits UL data through thesame time resource in the existing WLAN system, in the current WLANsystem, each of the plurality of STAs is unaware of transmission timingof the UL data of a different STA. Accordingly, it is difficult for anAP to receive the UL data on the same time resource from each of theplurality of STAs.

Furthermore, in the current WLAN system, frequency resources that areused for a plurality of STAs to transmit UL data may overlap. Forexample, if a plurality of STAs has different oscillators, a frequencyoffset may be generated. If a plurality of STAs having differentfrequency offsets performs UL transmission through different frequencyresources at the same time, some of frequency regions used by theplurality of STAs may overlap.

Furthermore, in the existing WLAN system, power control is not performedon each of a plurality of STAs. An AP may receive a signal havingdifferent power from each of a plurality of STAs depending on thedistance and a channel environment between the AP and each of theplurality of STAs. In this case, a signal reached with weak power maynot be detected by the AP compared to a signal reached with strongpower.

Method for Performing CCA

A clear channel assessment (CCA) method of an HE STA is described belowin more detail. As described above, an AP STA and a non-AP STA performCCA in order to determine the busy/idle state of a channel CCA indicatesa logical function/operation in the physical layer in which the currentuse state of a wireless medium (WM) is determined.

An STA performs CCA in the physical layer and reports a result of theexecution of CCA to the MAC layer. The STA may perform CCA in two modes,that is, CCA-energy detection (ED) and CCA-carrier sensing (CS). In anembodiment, the STA may determine the busy/idle state of a channel byperforming CCA-ED, performing CCA-CS, or using a combination of CCA-CSand CCA-ED. If CCA-CS and CCA-ED are combined, the STA may perform CCAby first performing CCA-CS and then performing CCA-ED or may perform CCAby first performing CCA-ED and then performing CCA-CS.

CCA-CS is performed through signal detection for a preamble. Thethreshold of CCA-CS is determined based on a minimum modulation and coderate sensitivity. Furthermore, a level of CCA-CS, that is, a thresholdvalue, may be set as a different value depending on a bandwidth. Forexample, in the case of 20 MHz channel spacing, an STA may determine achannel to be busy if the size of a received/obtained preamble signal(or CCA value) is −82 dBm or more. In the case of 10 MHz channelspacing, an STA may determine a channel to be busy if the size of areceived/obtained preamble signal (or CCA value) is −85 dBm or more. Inthe case of 5 MHz channel spacing, an STA may determine a channel to bebusy if the size of a received/obtained preamble signal (or CCA value)is −88 dBm or more. On the contrary, an STA may determine the channel tobe idle if the size of the received/obtained preamble signal (or CCAvalue) is less than the threshold (dBm) (e.g. −82 dBm, −85 dBm −88 dBm).In an embodiment, an STA may perform CCA-CS using the correlation ofSTFs in the preamble of an 802.11a signal. In this specification, a CCAthreshold/threshold value of an dBm unit may be called a CCA level. Inthis specification, CCA-CS may also be called CCA-signal detection (SD).

In the case of CCA-ED, an STA may determine a channel to be busy if aspecific signal is detected with intensity (dBm) of a threshold value ormore regardless of a signal defined in the 802.11 system. In this case,the threshold may be calculated as a value that is 20 dBm higher thanthat of CCA-CS. For example, an STA may determine a channel to be busyif a threshold is −62 dBm or more in the case of 20 MHz channel spacing.An STA may determine a channel to be busy if a threshold is −65 dBm ormore in the case of 10 MHz channel spacing. An STA may determine achannel to be busy if a threshold is −68 dBm or more in the case of 5MHz channel spacing.

A method described hereinafter may be applied to both CCA-CS and CCA-ED,but in the following embodiments, an example in which an STA performsCCA-CS is described.

If an STA and a system support a broadband, such as 20/40/80/160 MHz, adifferent CCA level may be applied to a primary channel and anon-primary channel (or a secondary channel). In this case, CCA levels(or threshold values) according to respective channel bandwidths may bedefined as in Table 5.

TABLE 5 Channel Signal threshold Signal threshold Energy thresholdbandwidth (primary) (non-primary) (non-primary)  20 Hz −82 dBm −72 dBm−62 dBm  40 MHz −79 dBm −72 dBm −59 dBm  80 MHz −76 dBm −69 dBm −86 dBm160 MHz −73 dBm n/a n/a

In Table 5, in the case of a 160 MHz channel, a corresponding signalthreshold/energy threshold is not defined because a secondary channel isnot present.

FIG. 8 is a conceptual diagram showing a method for performing CCAaccording to an embodiment of the present invention.

As described above, an efficient resource operation on the space may bedifficult because a CCA level, that is, a CCA threshold, is managed as afixed value within a single BSS for each channel bandwidth. In FIG. 8and the following embodiments, an AP 1 and an STA 1 may belong to afirst BSS, and an AP 2 and an STA 2 may belong to a second BSS.

Referring to FIG. 8, the AP 2 may send a PPDU to the STA 2 through a 20MHz channel. In this case, when a signal transmitted by the AP 2 isreceived by the AP 1 with signal intensity of −82 dBm or more, the AP 1determines the channel to be busy and does not send a signal to the STA1. However, in an environment in which the AP 1 and the STA 1 aresufficiently distant from the AP 2 or the STA 2 or interference from thesignal transmitted by the AP 1 does not have a great influence on theSTA 2, it is more efficient that the AP 1 sends the signal to the STA 1.That is, if a fixed CCA level is used, resource use efficiency on thespace is deteriorated. More specifically, this may be problematic if thefirst BSS to which the AP 1 and the STA 1 belong and the second BSS towhich the AP 2 and the STA 2 belong are overlapping basic service sets(OBSS) as shown in FIG. 8. In this case, the OBSS refers to BSSs inwhich some or all of the BSAs of different BSSs partially overlap andoperate on the same channel. Furthermore, an AP/STA placed in a BSAoverlapped between two BSSs is called an OBSS AP/STA.

Accordingly, an STA may perform spatial reuse (SR) (improvement onspatial efficiency) in which spatial resources are efficiently used bydynamically adjusting a CCA level according to a situation, determiningthe busy or idle state of a channel based on the adjusted CCA level, andtransmitting a signal. That is, the STA does not apply a uniform CCAlevel, but may adjust a CCA level low (or by reducing a criterion fordetermining the idle state of a channel) if the STA determines that itis not greatly influenced by interference attributable to a signaltransmitted by an STA (i.e., an OBSS STA) belonging to an OBSS, therebybeing capable of using transmission resources more efficiently.

In this case, in order for the STA to perform SR according to asituation (or in order to dynamically adjust a CCA level according to asituation), a criterion for calculating and adjusting a CCA level and arule by which a CCA level is managed need to be previously defined.Accordingly, this specification proposes an efficient method forsupporting the SR technology of an STA. More specifically, thisspecification proposes an efficient method for supporting the executionof the SR of an STA belonging to an OBSS in an UL 01-DMA environment.

In this specification, dynamic CCA means that a CCA level is adjustedaccording to a specific criterion instead of using a fixed CCA level andCCA is performed based on the adjusted CCA level. In the followingembodiments, a change of a CCA level may be applied to STAs belonging toan OBSS. Accordingly, spatial reuse efficiency of a bandwidth betweenSTAs belonging to an OBSS can be improved.

Method for Supporting Spatial Reuse (SR) Technology

This specification proposes a method for supporting the execution of theSR of an OBSS AP/STA by sending SR support information for supportingthe execution (or operation) of the efficient spatial reuse (SR) of STAs(more specifically, OBSS STAs).

The SR support information may include various pieces of controlinformation which are used for an OBSS AP/STA to perform SR. Forexample, the SR support information may include various pieces ofinformation for supporting the SR of an OBSS AP/STA, such as asensitivity for the interference of a victim STA (e.g., corresponding tothe receiver of on-going transmission, or an AP in the case of an ULtransmission procedure, or a STA in the case of DL transmissionprocedure), and/or an interference size or characteristic that itexperiences, and/or a margin value at which interference may betolerated (or the amount of interference permissible for the current MCSlevel) (or an acceptable interference level), and/or whether surroundingOBSS STAs will perform SR or not (i.e., whether the execution of the SRof OBSS STAs will be permitted), and/or a value at which OBSS STAs maychange or adjust a CCA level (i.e., CCA level adjustment information),and/or a CCA level and/or a TX power value (e.g., information regardingthat a victim STA sends a signal with power of what dB). Such SR supportinformation may also be called a “(first/second) SR support parametervalue.”

The SR support information may be transmitted to OBSS AP/STAs throughthe HE-SIG A field. The reason why the SR support information istransmitted through the HE-SIG A field other than the HE-SIG B field isthat the HE-SIG B field includes common or individual information for anintended user (or a specific/target STA) and thus OBSS AP/STAs areunable to be forced to decode the HE-SIG B field. However, the SRsupport information may be included in the HE-SIG A field andtransmitted because each of all of OBSS AP/STAs needs to decode theHE-SIG A field in order to determine whether a frame received by eachOBSS AP/STA is a myBSS frame or not (i.e., whether a received frame is aframe transmitted by an AP/STA belonging to the same BSS as each OBSSAP/STA).

Accordingly, in this specification, it is assumed that in the newlyproposed SR support method, the AP/STA of a specific BSS obtains the SRsupport information from the AP/STA of an OBSS (or the AP/STA of anotherBSS) through a received HE-SIG A field and performs SR for a PPDU lengthor TXOP duration indicated by the HE-SIG A field using the obtained SRsupport information.

In the 802.11ax system into which the OFDMA technology has beenintroduced, an AP sends a trigger frame in order to trigger UL MU OFDMAtransmission. In this case, the transmitted trigger frame includesvarious pieces of configuration information (or trigger information)about an UL MU PPDU (or an UL MU frame) to be transmitted by each STA.

A DL PPDU including a trigger frame is transmitted using only the HE-SIGA field of a PHY header. Accordingly, an AP may use MAC payload (or aMAC frame body) within a PSDU in order to send individualconfiguration/trigger information (i.e., user-specific configurationinformation) about each STA. Furthermore, if each of STAs that havereceived a trigger frame sends an UL PPDU (or an HE trigger-based PPDU),it needs to send an UL PPDU on which the same (or common) HE-SIG A fieldhas been loaded (because a method for generating the HE-SIG A field isindicated by the same trigger frame).

When such points are taken into consideration, the following problemsmay occur if the SR support information is transmitted to an OBSS AP/STAthrough the HE-SIG A field.

In an UL OFDMA transmission situation, efficient spatial reuse ispossible only when SR support information transmitted by STAs isindividually set by taking into consideration quality of a link betweeneach STA and an AP. However, the SR support information is identicallytransmitted by STAs because the HE-SIG A field carrying the SR supportinformation is identically transmitted by each STA. Accordingly, thereis ambiguity regarding how the SR support information identicallytransmitted by STAs will be configured (or set).

Accordingly, this specification proposes a method regarding how the SRsupport information identically transmitted by STAs through the HE-SIG Afield in common will be signaled in an UL OFDMA environment. Morespecifically, in an UL OFDMA environment, a victim STA is an AP.Accordingly, an AP, that is, a victim STA, sends SR indicationinformation which is used to generate the SR support information to betransmitted to an OBSS AP/STA through the trigger frame so that theexecution of the SR of the OBSS AP/STA can be supported moreefficiently.

In this specification, the SR indication information isindication/control information used to generate the SR supportinformation. The SR support information may be generated based on the SRindication information. The SR support information and the SR indicationinformation may be configured at least partially identically or at leastpartially differently depending on circumstances. For example, the SRindication information may include only the SR support information ormay include other indication control information for generating the SRsupport information along with the SR support information. If the SRindication information is configured identically with the SR supportinformation, the SR support information may be generated by duplicatingthe SR indication information without any change.

FIG. 9 is a flowchart illustrating a method for transmitting, by an STAapparatus, an UM MU PPDU according to an embodiment of the presentinvention. FIG. 10 is a conceptual diagram showing a method forperforming SR according to an embodiment of the present invention. InFIGS. 9 and 10, an AP (AP 1) and STA (STA 1 and/or 2) denote an AP andSTA associated with the same first BSS (BSS 1). An OBSS AP (AP 2) and/orSTA (STA 3) denote an AP and/or STA which are associated with a secondBSS (BSS 2) having a BSA overlapping the first BSS (BSS 1) and areplaced in the overlapped BSA.

Referring to FIGS. 9 and 10, first, the AP (AP 1) may transmit a triggerframe that requests UL MU transmission to a plurality of STAs (STA 1 and2) (S910). In this case, the trigger frame may include triggerinformation (or configuration information) for supporting the UL MUtransmission of a STA and SR indication information (or one or morefirst SR support parameter values) for indicating the SR of OBSS AP/STA(AP 2/STA 3) and generating SR support information (or one or moresecond SR support parameter values). The SR indication information istransmitted in a MAC payload of the trigger frame and is applied for theeach of the plurality of STAs in common.

As described above, in an UL OFMDA environment, a victim STA is an AP(AP 1). Accordingly, it is most efficient that the AP (AP 1), that is, avictim STA, directly generates SR permission information about the OBSSSTA (AP 2/STA 3), clear channel assessment (CCA) level adjustmentinformation about the OBSS STA (AP 2/STA 3), transmission powerinformation about the AP (AP 1), and interference level informationacceptable to the AP and provides them to the OBSS AP/STA (AP 2/STA 3).Accordingly, the AP (AP 1) generates SR indication information forgenerating SR support information to be provided to the OBSS AP/STA (AP2/STA 3) by taking into consideration the current channel situationand/or the current interference situation, etc., includes the SRindication information in a trigger frame, and sends the trigger frameto a plurality of STAs (STA 1 and 2) through DL. In this case, the SRindication information may be control information identicallytransmitted to the plurality of STAs (STA 1 and 2) so that the pluralityof STAs (STA 1 and 2) may generate the same SR support information. TheAP (AP 1) may generate an SR indication field (e.g., an HE-SIG A infofield) including the SR indication information, may include the SRindication field in the trigger frame, and may send the trigger frame tothe STAs (STA 1 and 2) through DL.

Next, each of the plurality of STAs (STA 1 and 2) may send an UL MU PPDU(e.g., an HE trigger-based PPDU, an UL MU frame), generated based on thereceived trigger frame, to the AP (AP 1) (S920). More specifically, eachof the plurality of STAs (STA 1 and 2) that has received the triggerframe may generate the UL MU PPDU, including a physical (PHY) preambleand a data field, based on trigger information included in the triggerframe. More specifically, the STA (STA 1 and/or 2) may generate SRsupport information (e.g., in a SR support subfield) included in aHE-SIG A field of the PHY preamble of the UL MU PPDU based on the SRindication information received through trigger frame. In other words,the HE-SIG A field in the UL MU PPDU (or UL MU frame) includes SRsupport information and the SR support information is set by using theSR indication information.

For example, the STA (STA 1 and/or 2) may generate the SR supportinformation by duplicating the received SR indication informationwithout change or generate the SR support information by processing theSR indication information according to an UL PPDU transmission formatand, may generate the HE-SIG A field including the corresponding SRsupport information. That is, while the SR support information isgenerally characterized as being generated based on the SR indicationinformation, the SR support information may be generated so that it isat least partially or even fully identical with the SR indicationinformation or at least partially different from the SR indicationinformation. In the case of at least partial identity between the SRindication information and the SR support information, at least one SRsupport parameter value is identically contained in both types ofinformation. The STA may send the UL MU PPDU into which the generatedHE-SIG A field has been inserted to the AP.

In this case, the OBSS AP/STA (AP 2/STA 3) may overhear (or receive) theUL MU PPDU transmitted by the STA (STA 2). In this case, the OBSS AP/STA(AP 2/STA 3) may denote an AP/STA (AP 2/STA 3) belonging to an OBSS withrespect to a BSS (BSS 1) to which the AP (AP 1) and STA (STA 1 and 2)sending the trigger frame belong. Furthermore, in this case, overhearingthe UL MU PPDU means that an UL MU PPDU transmitted by an STA (STA 2)belonging to a BSS (BSS 1) different from a BSS (BSS 2) to which (orwith which) the OBSS AP/STA (AP 2/STA 3) belongs (are associated) isreceived.

As described above, the OBSS AP/STA (AP 2/STA 3) may decode the HE-SIG Afield in order to check whether the received UL MU PPDU is the frame ofa BSS to which the OBSS AP/STA (AP 2/STA 3) belongs (checks a BSS colorfield). As a result, the OBSS AP/STA (AP 2/STA 3) overhears the HE-SIG Afield of the UL MU PPDU. As a result, the OBSS AP/STA (AP 2/STA 3) mayobtain the SR support information included in the HE-SIG A field.

That is, in conclusion, the STA (STA 2) may function to transfer the SRindication information, received from the AP (AP 1), to the OBSS AP/STA(AP 2/STA 3) as the SR support information. Furthermore, as describedabove, since the HE-SIG A field is identically transmitted to the STAs(STA 1 and 2) that have received the trigger frame, all of the OBSSAP/STAs (AP 2/STA 3) overhearing the UL MU PPDU transmitted based on thetrigger frame receive the same SR support information from the STAs (STA1 and 2).

Furthermore, although not shown in the flowchart of FIG. 9, the OBSSAP/STA (AP 2/STA 3) may overhear an UL SU PPDU, transmitted by an STAassociated with a different BSS, in addition to the UL MU PPDU. In thiscase, the HE-SIG A field of the UL SU PPDU may also include SR supportinformation as in the aforementioned embodiment. The OBSS AP/STA (AP2/STA 3) may perform SR based on the SR support information obtained bydecoding the HE-SIG A field.

Next, the OBSS AP/STA (AP 2/STA 3) may perform SR (S930). Morespecifically, the OBSS AP/STA (AP 2/STA 3) may perform SR based on theSR support information of the HE-SIG A field included in the overheard(or received) UL MU PPDU. For example, the OBSS AP/STA (AP 2/STA 3) mayadjust a CCA level, that is, a criterion for determining the busy oridle state of a channel, based on the overheard SR support information,may determine the state of the channel based on the adjusted CCA level,and may send a signal.

In accordance with the aforementioned flowchart, an AP (AP 1), that is,a victim STA, directly generates SR support information based on SRindication information generated by taking into consideration its owncapabilities, a surrounding interference situation, a channel situation,etc. Accordingly, there is an advantage in that SR support informationhaving the highest reliability is transmitted assuming that the same SRsupport information is transmitted to all of OBSS AP/STAs (AP 2/STA 3).Furthermore, if SR support information is generated identically with SRindication information, an STA (STA 1 and 2) may generate SR supportinformation by duplicating the SR indication information receivedthrough a trigger frame without any change. Accordingly, there is anadvantage in that a procedure for generating the SR support informationbecomes very simple.

The HE-SIG A field of an UL MU PPDU may be configured to include only SRsupport information. In this case, it may be said that “the HE-SIG Afield of the UL MU PPDU is generated based on SR indicationinformation.” Furthermore, if SR support information is generatedidentically with SR indication information, it may be said that “theHE-SIG A field of an UL MU PPDU may be configured to include the SRindication information received through a trigger frame.”

As described above, the SR indication information may be transmitted toSTAs (STA 1 and 2) through the trigger frame. A detailed method forsignaling such SR indication information within a trigger frame needs tobe determined. Accordingly, a method for efficiently signaling the SRindication information is hereinafter proposed. Prior to a descriptionof the method, the structure of the trigger frame is first describedbelow.

FIG. 11 is a diagram showing the structure of the trigger frameaccording to an embodiment of the present invention.

Referring to FIG. 11, the trigger frame may include a Frame Controlfield, a Duration field, an RA field, a TA field, a Common Info field(or a common information field), a Per User (STA) Info N field (or auser-specific field and an STA Info N field), padding bits, and FCS. Thepresent invention is not limited to such fields, and some of the fieldsincluded in the trigger frame may be excluded or a new field may beadded to the trigger frame.

The RA field indicates the address of a reception STA (or the address ofan intended user/STA) that receives the trigger frame. The RA field maybe included in or excluded from the trigger frame depending on anembodiment.

The TA field indicates the address of an STA that sends the triggerframe.

The Common Info field indicates a field including common controlinformation which is received in common by STAs that receive the triggerframe. The Common Info field may include trigger type information, ULPPDU length information, BW information, GI information, LTF typeinformation, LTF Num (number) information and/or sounding dialog tokeninformation. In this case, the UL PPDU length information indicates a(maximum) length of an UL MU PPDU triggered by the trigger frame. The BWinformation indicates the transmission bandwidth of a corresponding ULMU PPDU. The GI information indicates a guard interval applied to acorresponding UL MU PPDU (or indicates a guard interval when acorresponding UL MU PPDU is generated). The LTF type informationindicates the LTF type of a corresponding UL MU PPDU. The LTF Numinformation indicates the number of an HE-LTF included in acorresponding UL MU PPDU. The sounding dialog token informationindicates a sounding dialog token number.

The Per User Info N field indicates a field including STA-specificcontrol information that is individually received by each STA.Accordingly, the number of Per User Info N fields corresponding to thenumber of STAs may be included in the trigger frame. The Per User Info Nfield may include AID information of an STA that receives acorresponding field and MCS information, coding information, feedbacktype information, Nc index information, Nr index information, andcodebook information which are used for an STA to generate/send an UL MUframe.

The structure of the trigger frame has been described above. A methodfor signaling the SR indication information is described below. Thisspecification proposes i) a PHY signaling method, ii) an MAC signalingmethod, and iii) a hybrid signaling method, that is, methods forsignaling the SR indication information.

1. PHY Signaling Method

In accordance with a first embodiment of the present invention, SRindication information may be signaled in the PHY preamble. That is, theSR indication information may be included in the PHY preamble of a DL MUPPDU that carries a trigger frame and may be transmitted to STAs. Morespecifically, the SR indication information may be included in theHE-SIG A field of the PHY preamble of the DL MU PPDU and transmitted.

SR support information transmitted from each STA to an OBSS AP/STAthrough the HE-SIG A field of an UL MU PPDU may be generated based on SRindication information which is transmitted through the HE-SIG A fieldof a DL MU PPDU including a trigger frame transmitted by an AP.

For example, SR support information transmitted from each STA to an OBSSAP/STA may be generated substantially identically with SR indicationinformation transmitted from an AP to the corresponding STA. In thiscase, the SR support information transmitted by the STA in an HE-SIG Afield through UL may be generated/configured by duplicating the SRindication information of the HE-SIG A field transmitted from the AP tothe corresponding STA through DL. Accordingly, the SR indicationinformation transmitted through the HE-SIG A field of a trigger frameand the SR support information transmitted through the HE-SIG A field ofan UL frame transmitted after the trigger frame may be the same (or maybe substantially the same), but the present invention is not limitedthereto. For example, the SR support information may be configureddifferently from the SR indication information.

The SR indication information may be generated (or configured) by takinginto consideration the worst case in which a link that belongs to linksbetween an AP and STAs that will perform UL transmission and that hasthe worst link quality or is most sensitive to interference.Alternatively, the SR indication information may be configured by takinginto consideration the mean case of a link that belongs to links betweenan AP and STAs that will perform UL transmission and that has averagelink quality or has a mean influence of interference.

2. MAC Signaling Method

In accordance with a second embodiment of the present invention, SRindication information may be signaled through the MAC frame (or MACpayload) of a DL MU PPDU. More specifically, the SR indicationinformation may be signaled in an MAC frame (or MAC payload)corresponding to a trigger frame and may be transmitted to each STA. Inthis case, the SR indication information may be identically transmittedto a plurality of STAs so that the plurality of STAs can generate thesame SR support information. To this end, the SR indication informationmay be included in the Common Info field of the trigger frame andtransmitted so that it is received in common by the plurality of STAswhich receive the trigger frame.

SR support information transmitted from STAs to an OBSS AP/STA throughthe HE-SIG A field of an UL MU PPDU (or an UL MU frame) may be generatedbased on SR indication information received by the corresponding STAsthrough a trigger frame.

For example, SR support information transmitted from STAs to an OBSSAP/STA may be generated substantially identically with SR indicationinformation transmitted from an AP to the corresponding STAs. This maybe said that SR support information transmitted by STAs in UL using anHE-SIG A field is generated and configured by duplicating SR indicationinformation transmitted by the AP using a trigger frame in DL, but thepresent invention is not limited thereto. The SR support information maybe configured differently from the SR indication information.

The SR indication information may be included in the SR indication fieldof a trigger frame, and the SR support information may be included inthe SR support subfield of an HE-SIG A field. Accordingly, the SRsupport subfield (or an HE-SIG A/Spatial Reuse subfield) in which an ULMU PPDU (or an UL MU frame) is transmitted to an OBSS AP/STA may beset/configured based on content (or a value) indicated by an SRindication field (or n HE-SIG A Info/Spatial Reuse field) included inthe trigger frame. In this case, the content (or value) indicated by theSR indication information field may correspond to the SR supportinformation (or an SR support parameter value). If the SR supportinformation is generated identically with the SR indication information,the content (or value) indicated by the SR indication information fieldmay correspond to the SR indication information.

The SR indication information may be transmitted as a single value sothat it is applied to STAs in common. This may be said that a singlepiece of SR indication information is transmitted through a triggerframe. Alternatively, if the HE-SIG A field of an UL MU PPDU (or UL MUframe) transmitted by each STA is not duplicated (or is not identicallytransmitted) or SR support/indication information can individuallyoperate for each STA, the SR indication information may be transmittedwith a plurality of values so that each STA can configure/applydifferent SR indication information. In this case, the SR indicationinformation may be included in the Per User Info N field of the triggerframe and transmitted to each STA.

If SR indication information is transmitted with a plurality of valuesas described above, the SR indication information and the SR supportinformation of an UL MU PPDU to be subsequently transmitted by aplurality of STAs may have different values or SR support informationtransmitted by each of a plurality of STAs in UL may have a differentvalue.

A single piece of SR indication information transmitted through atrigger frame may be generated (or configured) by taking intoconsideration the worst case in which a link that belongs to linksbetween an AP and STAs that will perform UL transmission and that hasthe worst link quality or is most sensitive to interference.Alternatively, the corresponding SR indication information may beconfigured by taking into consideration the mean case of a link thatbelongs to links between an AP and STAs that will perform ULtransmission and that has average link quality or has a mean influenceof interference.

The second embodiment has an advantage in that it has smaller signalingoverhead than the first embodiment. A trigger frame corresponds to abroadcast frame in common received (or decoded) by a plurality of STAs.Accordingly, if SR indication information is once inserted into thetrigger frame, STAs which have received a DL MU PPDU carrying thetrigger frame receive the same SR indication information at once.

In contrast, in accordance with the first embodiment, the SR indicationinformation needs to be signaled in the HE-SIG A field. As describedabove, the same SR indication information is also duplicated andtransmitted in a 20 MHz unit because the HE-SIG A field is identicallyduplicated and transmitted in a 20 MHz unit. Accordingly, in accordancewith the second embodiment, there is a problem in that signalingoverhead for the SR indication information is increased by the number ofduplications of the HE-SIG A field. If a DL MU PPDU is transmittedthrough an 80 MHz channel, signaling overhead is increased that muchbecause SR indication information is duplicated four times andtransmitted.

Accordingly, the second embodiment has an advantage in that it hassmaller signaling overhead for SR indication information than the firstembodiment. Accordingly, if the bit size of a trigger frame issufficient, the SR indication information may be signaled in the triggerframe. However, the present invention is not limited to such an example.For example, the SR indication information may be signaled in the HE-SIGA field if the bit size of the trigger frame is not sufficient or thebit size of the SR indication information is small.

3. Hybrid Signaling Method

In accordance with a third embodiment of the present invention, SRindication information may be signaled by a combination of the first andthe second embodiments. That is, the SR indication information may besignaled in the PHY preamble and the MAC frame.

For example, if there is a difference between SR indication informationand SR support information, the SR indication information (or a first SRsupport parameter value) may be signaled in the PHY preamble (e.g., theHE-SIG A field) according to the first embodiment. A difference betweenSR indication information (or a second SR support parameter value) andSR support information (or an SR support parameter) to be transmitted byeach STA (i.e., a differential value between the first and the second SRsupport parameter values) may be signaled in a trigger frame.

Furthermore, if the HE-SIG A field of an UL MU PPDU (or an UL frame)transmitted by each STA is not duplicated (or identically transmitted)or SR indication information is capable of individual operation for eachSTA, a trigger frame may individually indicate a difference between theSR indication information and SR indication information to betransmitted by each STA in UL for each STA. In this case, the SRindication information may be included in the Per User Info N field ofthe trigger frame for each STA and transmitted.

As described above, the SR indication information may be signaled invarious ways in accordance with the proposed first to third embodimentsof the present invention or a combination of them, and may betransmitted from an AP, that is, a victim STA, to an OBSS AP/STA as SRsupport information. The OBSS AP/STA may determine whether or not toperform SR based on the SR support information received as describedabove and may efficiently use spatial resources.

In this specification, an embodiment in which SR support information istransmitted through an UL MU PPDU transmitted as a response to a DL MUPPDU including a trigger frame has been described, for convenience ofdescription. However, the preset invention is not limited to the UL MUPPDU. The aforementioned descriptions may be identically applied to aPPDU including the HE-SIG A field regardless of a PPDU format.Accordingly, the HE-SIG A field of the PPDU may include SR supportinformation, and an OBSS AP/STA that has received the HE-SIG A field ofthe corresponding PPDU may obtain the SR support information.

FIG. 12 is a block diagram of each STA apparatus according to anembodiment of the present invention.

Referring to FIG. 12, the STA apparatus (or STA) 1210 may include memory1212, a processor 1211, and a radio frequency (RF) unit 1213.Furthermore, as described above, the STA apparatus 1210 is an HE STAapparatus and may be an AP STA or a non-AP STA.

The RF unit 1213 is connected to the processor 1211 and maytransmit/receive radio signals. The RF unit 1213 may up-convert data,received from the processor 1211, into a transmission/reception band,and may transmit a signal.

The processor 1211 is connected to the RF unit 1213 and may implementthe physical layer and/or the MAC layer according to the IEEE 802.11system. The processor 1211 may be configured to perform operationsaccording to the various embodiments of the present invention based onthe drawings and description. Furthermore, a module for implementing theoperations of the STA 1210 according to the various embodiments of thepresent invention may be stored in the memory 1212 and may be executedby the processor 1111.

The memory 1212 is connected to the processor 1211 and stores variouspieces of information for driving the processor 1211. The memory 1212may be included in the processor 1211 or may be installed outside theprocessor 1211, and may be connected to the processor 1211 by the knownmeans.

Furthermore, the STA apparatus 1210 may include a single antenna ormultiple antennas.

A detailed configuration of the STA apparatus 1210 of FIG. 12 may beimplemented so that the various embodiments of the present invention areindependently applied to the configuration or two or more of the variousembodiments are applied to the configuration at the same time. Morespecifically, the processor 1211 of the STA apparatus may be implementedto perform the aforementioned embodiments.

Furthermore, the terms described in the embodiments of the presentinvention may be substituted with other terms according to circumstancesand are not limited to the aforementioned terms. Accordingly, although adifferent term is used, it may be considered as indicating the sameobject if it has the same function.

In the aforementioned embodiments, the elements and characteristics ofthe present invention have been combined in specific forms. Each of theelements or characteristics should be considered to be optional unlessotherwise described explicitly. Each of the elements or characteristicsmay be implemented without being combined with other elements orcharacteristics. Furthermore, some of the elements and/or thecharacteristics may be combined to form an embodiment of the presentinvention. The sequence of the operations described in connection withthe embodiments of the present invention may be changed. Some ofelements or characteristics in an embodiment may be included in anotherembodiment or may be substituted with corresponding elements orcharacteristics in another embodiment. It is evident that in the claims,claims not having an explicit citation relation may be combined to formone or more embodiments or may be included as one or more new claims byamendments after filing an application.

An embodiment of the present invention may be implemented by variousmeans, for example, hardware, firmware, software or a combination ofthem. In the case of implementations by hardware, an embodiment of thepresent invention may be implemented using one or moreApplication-Specific Integrated Circuits (ASICs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, microcontrollers and/ormicroprocessors.

In the case of an implementation by firmware or software, an embodimentof the present invention may be implemented in the form of a module,procedure, or function for performing the aforementioned functions oroperations. Software code may be stored in memory and driven by aprocessor. The memory may be placed inside or outside the processor, andmay exchange data with the processor through a variety of known means.

It is evident to those skilled in the art that the present invention maybe materialized in other specific forms without departing from theessential characteristics of the present invention. Accordingly, thedetailed description should not be construed as being limitative fromall aspects, but should be construed as being illustrative. The scope ofthe present invention should be determined by reasonable analysis of theattached claims, and all changes within the equivalent range of thepresent invention are included in the scope of the present invention.

INDUSTRIAL APPLICABILITY

Although the frame transmission method in a wireless communicationsystem according to the embodiments of the present invention has beendescribed based on an example in which the method is applied to the IEEE802.11 system, it may also be applied to various other wirelesscommunication systems in addition to the IEEE 802.11 system.

1. A method for indicating, by an access point (AP) associated with a first basic service set (BSS), spatial reuse (SR) in a wireless LAN (WLAN) system, the method comprising: transmitting a trigger frame which requests uplink multi-user (UL MU) transmission of a plurality of stations (STAs); and receiving an UL MU physical protocol data unit (PPDU) generated based on the trigger frame from the plurality of STAs, wherein: the trigger frame comprises SR indication information for indicating the SR of an overlapping BSS (OBSS) STA, and a first high efficiency (HE)-signal (SIG) A field of the UL MU PPDU comprises SR support information generated based on the SR indication information.
 2. The method of claim 1, wherein: the trigger frame comprises a Common Info field comprising common control information about a plurality of STAs receiving the trigger frame and a Per User Info field comprising STA-specific control information about each of the plurality of STAs, and the SR indication information is included in the Common Info field of the trigger frame.
 3. The method of claim 2, if the AP is placed in an OBSS in which the first BSS and a second BSS overlap, further comprising: receiving a second HE-SIG A field of a PPDU transmitted by an STA placed in the second BSS; obtaining SR support information of the second HE-SIG A field; and performing the SR based on the SR support information.
 4. The method of claim 3, wherein the performing the SR comprises: adjusting a clear channel assessment (CCA) level; and determining a busy or idle state of a channel based on the adjusted CCA level.
 5. The method of claim 4, wherein the determining the busy or idle state of the channel based on the adjusted CCA level comprises: obtaining a CCA value by performing CCA on the channel; if the CCA value is greater than the adjusted CCA level, determining the busy state of the channel; and if the CCA value is less than the adjusted CCA level, determining the idle state of the channel.
 6. The method of claim 3, wherein the SR is performed during a length of the PPDU.
 7. The method of claim 2, wherein the SR support information comprises at least one of SR permission information of the OBSS STA, transmission power information of the AP, and information about an interference level acceptable to the AP.
 8. A method for indicating, by a station (STA) associated with a first basic service set (BSS), spatial reuse (SR) in a wireless LAN (WLAN) system, the method comprising: receiving a trigger frame which requests uplink multi-user (UL MU) transmission of a plurality of stations (STAs) from an access point (AP); and generating an UL MU physical protocol data unit (PPDU) generated based on the trigger frame, wherein the trigger frame comprises SR indication information for indicating the SR of an overlapping BSS (OBSS) STA, and a first high efficiency (HE)-signal (SIG) A field of the UL MU PPDU comprises SR support information generated based on the SR indication information.
 9. The method of claim 8, wherein: the trigger frame comprises a Common Info field comprising common control information about a plurality of STAs receiving the trigger frame and a Per User Info field comprising STA-specific control information about each of the plurality of STAs, and the SR indication information is included in the Common Info field of the trigger frame.
 10. The method of claim 9, if the STA is placed in an OBSS in which the first BSS and a second BSS overlap, further comprising: receiving a second HE-SIG A field of a PPDU transmitted by an STA placed in the second BSS; obtaining SR support information of the second HE-SIG A field; and performing the SR based on the SR support information.
 11. The method of claim 10, wherein the performing the SR comprises: adjusting a clear channel assessment (CCA) level; and determining a busy or idle state of a channel based on the adjusted CCA level.
 12. The method of claim 11, wherein the determining the busy or idle state of the channel based on the adjusted CCA level comprises: obtaining a CCA value by performing CCA on the channel; if the CCA value is greater than the adjusted CCA level, determining the busy state of the channel; and if the CCA value is less than the adjusted CCA level, determining the idle state of the channel.
 13. The method of claim 10, wherein the SR is performed during a length of the PPDU.
 14. The method of claim 9, wherein the SR support information comprises at least one of SR permission information of the OBSS STA, transmission power information of the AP, and information about an interference level acceptable to the AP.
 15. A station (STA) associated with a first basic service set (BSS) in a wireless LAN (WLAN) system, the STA comprising: a radio frequency (RF) unit configured to transmit and receive radio signals; and a processor configured to control the RF unit, wherein: the STA is configured to receive a trigger frame which requests uplink multi-user (UL MU) transmission of a plurality of stations (STAs) and generates an UL MU physical protocol data unit (PPDU) generated based on the trigger frame from the plurality of the STAs, wherein the trigger frame comprises SR indication information for indicating the SR of an overlapping BSS (OBSS) STA, and wherein a first high efficiency (HE)-signal (SIG) A field of the UL MU PPDU comprises SR support information generated based on the SR indication information.
 16. The STA of claim 15, wherein the trigger frame comprises a Common Info field comprising common control information about a plurality of STAs receiving the trigger frame and a Per User Info field comprising STA-specific control information about each of the plurality of STAs, and the SR indication information is included in the Common Info field of the trigger frame.
 17. The STA of claim 15, wherein if the STA is placed in an OBSS in which the first BSS and a second BSS overlap, the STA is further configured to: receive a second HE-SIG A field of a PPDU transmitted by another STA placed in the second BSS, obtain SR support information of the second HE-SIG A field, and perform the SR based on the SR support information. 